1. Field of the Invention
The present invention relates to a fixing apparatus and an image formation apparatus, and in particular to technology for preventing deterioration of image quality in a fixing apparatus.
2. Related Art
An electrophotographic-type image formation apparatus, after causing toner to be electrostatically adsorbed to a charged recording sheet, causes the toner to be fused to the recording sheet by a fixer. To fix the toner, in order to pass the recording sheet through a heating roller and a pressurizing roller, the heating roller is charged by the charged recording sheet.
As a result, there are cases in which image quality deteriorates due to electrostatic offset of the toner on the recording sheet being electrostatically adsorbed to the heating roller, or discharge occurring when the recording sheet is ejected from the fixer (hereinafter, such image quality deterioration is referred to as “sheet back end separation discharge noise”).
Measures against this type of problem include, for example, impressing a bias voltage on the heating roller, pressing an electrically conductive material to the heating roller and neutralizing the heating roller, or pressing an electrically conductive material to the recording sheet to which toner has been transferred and neutralizing the recording sheet (for example, see Japanese Patent Application Publication No. 2005-55786). By doing this, the charge of the heating roller can be lessened, and the occurrence of electrostatic offset can be suppressed.
However, demand for miniaturization and reduced cost of image formation apparatuses continues to increase, and it must be noted that providing material for neutralizing the heating roller or the recording sheet and material for impressing a bias voltage on the heating roller, as in conventional technology, are contrary to such demands.
Also, since the heating roller rotates at the time of image formation, and the recording sheet, needless to say, moves along a conveyance path, a strong frictional force operates on the neutralizing materials in contact with the heating roller and the recording sheet. Also, the same is true for the materials for impressing a voltage on the heating roller. For this reason, such materials unavoidably deteriorate with the passage of time, leading to deterioration of image quality with the passage of time.
Furthermore, technical difficulties caused by high temperature occur when impressing voltage on the heating roller.